entc/gen: introduce validation errors (#547)

This introduces the concept of validation errors, where we have a high
level validation error which wraps a more detailed error message.

The higher level `ValidationError` is set up in the generated files, much
like the `NotFoundError` and `ConstraintError` and is accompanied by an
`IsValidationError` check method. Thus, it can be used as follows:

```go
t, err := tx.Team.Create().SetName(input.Name).Save(ctx)
if ent.IsValidationError(err) {
        // handle validation error response
}
```

examples/start/ent/car_create.go

@@ -64,10 +64,10 @@ func (cc *CarCreate) Mutation() *CarMutation {
 // Save creates the Car in the database.
 func (cc *CarCreate) Save(ctx context.Context) (*Car, error) {
 	if _, ok := cc.mutation.Model(); !ok {
-		return nil, errors.New("ent: missing required field \"model\"")
+		return nil, &ValidationError{Name: "model", err: errors.New("ent: missing required field \"model\"")}
 	}
 	if _, ok := cc.mutation.RegisteredAt(); !ok {
-		return nil, errors.New("ent: missing required field \"registered_at\"")
+		return nil, &ValidationError{Name: "registered_at", err: errors.New("ent: missing required field \"registered_at\"")}
 	}
 	var (
 		err  error

examples/start/ent/car_update.go

@@ -319,7 +319,7 @@ func (cuo *CarUpdateOne) sqlSave(ctx context.Context) (c *Car, err error) {
 	}
 	id, ok := cuo.mutation.ID()
 	if !ok {
-		return nil, fmt.Errorf("missing Car.ID for update")
+		return nil, &ValidationError{Name: "ID", err: fmt.Errorf("missing Car.ID for update")}
 	}
 	_spec.Node.ID.Value = id
 	if value, ok := cuo.mutation.Model(); ok {

examples/start/ent/ent.go

@@ -100,6 +100,31 @@ func Sum(field string) AggregateFunc {
 	}
 }
 
+// ValidationError returns when validating a field fails.
+type ValidationError struct {
+	Name string // Field or edge name.
+	err  error
+}
+
+// Error implements the error interface.
+func (e *ValidationError) Error() string {
+	return e.err.Error()
+}
+
+// Unwrap implements the errors.Wrapper interface.
+func (e *ValidationError) Unwrap() error {
+	return e.err
+}
+
+// IsValidationError returns a boolean indicating whether the error is a validaton error.
+func IsValidationError(err error) bool {
+	if err == nil {
+		return false
+	}
+	var e *ValidationError
+	return errors.As(err, &e)
+}
+
 // NotFoundError returns when trying to fetch a specific entity and it was not found in the database.
 type NotFoundError struct {
 	label string

examples/start/ent/group_create.go

@@ -53,11 +53,11 @@ func (gc *GroupCreate) Mutation() *GroupMutation {
 // Save creates the Group in the database.
 func (gc *GroupCreate) Save(ctx context.Context) (*Group, error) {
 	if _, ok := gc.mutation.Name(); !ok {
-		return nil, errors.New("ent: missing required field \"name\"")
+		return nil, &ValidationError{Name: "name", err: errors.New("ent: missing required field \"name\"")}
 	}
 	if v, ok := gc.mutation.Name(); ok {
 		if err := group.NameValidator(v); err != nil {
-			return nil, fmt.Errorf("ent: validator failed for field \"name\": %w", err)
+			return nil, &ValidationError{Name: "name", err: fmt.Errorf("ent: validator failed for field \"name\": %w", err)}
 		}
 	}
 	var (

examples/start/ent/group_update.go

@@ -77,7 +77,7 @@ func (gu *GroupUpdate) RemoveUsers(u ...*User) *GroupUpdate {
 func (gu *GroupUpdate) Save(ctx context.Context) (int, error) {
 	if v, ok := gu.mutation.Name(); ok {
 		if err := group.NameValidator(v); err != nil {
-			return 0, fmt.Errorf("ent: validator failed for field \"name\": %w", err)
+			return 0, &ValidationError{Name: "name", err: fmt.Errorf("ent: validator failed for field \"name\": %w", err)}
 		}
 	}
 
@@ -256,7 +256,7 @@ func (guo *GroupUpdateOne) RemoveUsers(u ...*User) *GroupUpdateOne {
 func (guo *GroupUpdateOne) Save(ctx context.Context) (*Group, error) {
 	if v, ok := guo.mutation.Name(); ok {
 		if err := group.NameValidator(v); err != nil {
-			return nil, fmt.Errorf("ent: validator failed for field \"name\": %w", err)
+			return nil, &ValidationError{Name: "name", err: fmt.Errorf("ent: validator failed for field \"name\": %w", err)}
 		}
 	}
 
@@ -322,7 +322,7 @@ func (guo *GroupUpdateOne) sqlSave(ctx context.Context) (gr *Group, err error) {
 	}
 	id, ok := guo.mutation.ID()
 	if !ok {
-		return nil, fmt.Errorf("missing Group.ID for update")
+		return nil, &ValidationError{Name: "ID", err: fmt.Errorf("missing Group.ID for update")}
 	}
 	_spec.Node.ID.Value = id
 	if value, ok := guo.mutation.Name(); ok {

examples/start/ent/user_create.go

@@ -83,11 +83,11 @@ func (uc *UserCreate) Mutation() *UserMutation {
 // Save creates the User in the database.
 func (uc *UserCreate) Save(ctx context.Context) (*User, error) {
 	if _, ok := uc.mutation.Age(); !ok {
-		return nil, errors.New("ent: missing required field \"age\"")
+		return nil, &ValidationError{Name: "age", err: errors.New("ent: missing required field \"age\"")}
 	}
 	if v, ok := uc.mutation.Age(); ok {
 		if err := user.AgeValidator(v); err != nil {
-			return nil, fmt.Errorf("ent: validator failed for field \"age\": %w", err)
+			return nil, &ValidationError{Name: "age", err: fmt.Errorf("ent: validator failed for field \"age\": %w", err)}
 		}
 	}
 	if _, ok := uc.mutation.Name(); !ok {

examples/start/ent/user_update.go

@@ -129,7 +129,7 @@ func (uu *UserUpdate) RemoveGroups(g ...*Group) *UserUpdate {
 func (uu *UserUpdate) Save(ctx context.Context) (int, error) {
 	if v, ok := uu.mutation.Age(); ok {
 		if err := user.AgeValidator(v); err != nil {
-			return 0, fmt.Errorf("ent: validator failed for field \"age\": %w", err)
+			return 0, &ValidationError{Name: "age", err: fmt.Errorf("ent: validator failed for field \"age\": %w", err)}
 		}
 	}
 
@@ -411,7 +411,7 @@ func (uuo *UserUpdateOne) RemoveGroups(g ...*Group) *UserUpdateOne {
 func (uuo *UserUpdateOne) Save(ctx context.Context) (*User, error) {
 	if v, ok := uuo.mutation.Age(); ok {
 		if err := user.AgeValidator(v); err != nil {
-			return nil, fmt.Errorf("ent: validator failed for field \"age\": %w", err)
+			return nil, &ValidationError{Name: "age", err: fmt.Errorf("ent: validator failed for field \"age\": %w", err)}
 		}
 	}
 
@@ -477,7 +477,7 @@ func (uuo *UserUpdateOne) sqlSave(ctx context.Context) (u *User, err error) {
 	}
 	id, ok := uuo.mutation.ID()
 	if !ok {
-		return nil, fmt.Errorf("missing User.ID for update")
+		return nil, &ValidationError{Name: "ID", err: fmt.Errorf("missing User.ID for update")}
 	}
 	_spec.Node.ID.Value = id
 	if value, ok := uuo.mutation.Age(); ok {